In optical systems, and in particular in imaging systems, such as thermal cameras, it is needed to provide a shutter that can be placed in front of the imaging sensor and block its view when desired. In an Infra-Red (IR) camera a shutter is provided for occasional calibration of the imaging sensor, or for preventing undesired irradiation from reaching the imaging sensor.
Calibration is necessary in thermal sensors in order to ensure accurate measurements and to obtain correct images. Calibration is especially important in IR cameras, which have a thermal sensor that is not cooled to supercool temperatures.
Every once in a while a uniform surface of a black body is placed in front of the sensor and the sensor matrix is calibrated to measure a surface of uniform temperature. There are known IR cameras, which include seen an optical shutter. Typically the shutter comprises a black painted plate, which is displaced between two positions in front of the sensor, a blocking position in front of the sensor view and a retracted position, where the shutter is removed from the sensor's field of view.
A known shutter mechanism includes a shutter plate turning about a motor axis to and out of the blocking position. Another shutter mechanism includes a shutter plate coupled to a motor with linear transmission so as to facilitate linear motion of the shutter between the two positions. In some cases it is desired to have a shutter mechanism that is silent in order to prevent exposing the existence and location of the imaging system.
A staring array, staring-plane array, Focal-Plane Array (FPA), or focal-plane is an image sensing device consisting of an array (typically rectangular) of light-sensing pixels at the focal plane of a lens. FPAs are used most commonly for imaging purposes for example taking pictures or video imagery, but can also be used for non-imaging purposes such as spectrometry, LIDAR (Light Detection And Ranging), and wave-front sensing.
The focal plane arrays in IR camera cores must be calibrated periodically, and to execute the calibration process, the focal plane array is presented with a uniform IR source. This is typically accomplished by covering the focal plane array window with a uniform temperature, uniform emissivity plate, which is commonly referred to as a shutter. It is important that the shutter be as close to the window as possible to eliminate any stray IR energy entry into the chamber, especially for wide field of view applications. It is also important that the shutter and movement mechanism not intrude on the space in front of the lens assembly. The lens assembly must be placed as close to the sensor element as possible to minimize the size and cost of the lens assembly.
A need therefore exists for an improved space saving, lower cost, linear motor drive for a sliding IR camera shutter.